Merkelrakkudest

Merkelrakkudest, also known as Merkel cells, are specialized mechanoreceptor cells embedded in the epidermis of mammalian skin. They are located in the basal layer, with particularly high densities in regions of fine tactile discrimination such as fingertips, lips, and the face. Merkel cells form intimate associations with afferent nerve endings, creating Merkel cell-neurite complexes essential for touch sensations.

Morphology and markers: Merkel cells are oval to round, small cells containing dense-core granules. In humans they express cytokeratin 20 in a perinuclear dot pattern and exhibit neuroendocrine markers, reflecting their hybrid epithelial-neuronal character and their role in sensory signaling.

Function: Merkel cells contribute to the sense of light touch and fine tactile acuity by mediating slowly adapting responses to sustained pressure and texture. They release signaling molecules that influence the adjacent nerve fibers, enabling precise discrimination of shape, texture, and spatial details.

Development and origin: The precise developmental origin of Merkel cells has been debated. Evidence supports both epidermal progenitor origins and neural crest contributions; development involves transcription factors such as Atoh1. Their formation is tightly linked to the establishment of Merkel cell-neurite complexes with cutaneous nerves.

Clinical relevance: Merkel cell carcinoma is a rare but aggressive skin cancer historically linked to Merkel cells or their precursors. It is associated with Merkel cell polyomavirus in many cases. Diagnosis uses histology and immunohistochemistry, with CK20-positive, TTF-1-negative staining; treatment often includes surgery, radiation, and immunotherapy.